The publication DE 103 04 479 B3 is known to be the closest prior art. This describes a device for transmitting and receiving data for remote controls for hearing devices. It shows how a combined transmit/receive unit can be realized with a single transmit/receive antenna, without overloading the downstream receiver. Standard silicon protective diodes are used here, which function well at low frequencies and comparatively high resonant capacitances, their blocking capacitance being negligible. These diodes are necessary in order to limit the voltage at the input of the receive circuit in the transmit instance. They are therefore essential for the combined transmit/receive circuit.
It is necessary also to be able to deal with higher bandwidths with the transmit/receive circuits of hearing devices. However with the known device for the transmission of higher bandwidths described above, as soon as a switch is made to higher frequencies, smaller inductances and also smaller capacitances are deployed. This means that the blocking capacitances of the protective diodes are no longer negligible and they detune the resonant circuit in the receive element significantly. Moreover the blocking capacitances of the diodes are not known and can vary with the manufacturing process. This makes a clean tuning of the oscillating circuit in the receive element very difficult, so it would have to be carried out manually on an individual basis in each device with a high level of outlay. It is not possible to dispense with said diodes however, as they are absolutely essential as input protection elements for the receive amplifier. Without protection very high voltages would occur at the input of the receive amplifier in the transmit instance, leading to destruction of the receive amplifier.
The further publication EP 1 301 017 A1 describes a mobile communication device with electrostatic discharge protection. Two PIN diodes are connected in an anti-parallel manner between the high-frequency input of the receiver and ground. They serve as overvoltage protection and are characterized by their minimal effect on high-frequency signals due to their very low capacitance.